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| Titel |
A Lunar-like Chronology Model as Estimator for the Mass Depletion of the Asteroid Belt |
| VerfasserIn |
Oliver Hartman, Gerhard Neukum |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250058033
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| Zusammenfassung |
| The bombardment of the Solar System by small bodies over the past 4.5Â Ga is documented
by the impact cratering-record of the surfaces of planetary bodies. The cratering record of
Earth’s moon revealed a typical size frequency-distribution (SFD), which has led to
well-known impact cratering chronology models. Comparisons of the SFD of the Near Earth
Asteroids (NEA) and magnitude-derived diameter estimates have led to the conclusion that
the Asteroid Belt acts as the primary source of projectiles impacting the surfaces of planetary
bodies of the Inner Solar System, for the Outer Solar System this is still under
debate.
To support the hypothesis that the Asteroid Belt acts as the main source for projectiles
impacting planetary surfaces of both the Inner and Outer Solar System, comparisons of the
total impacted projectiles and masses on planetary surfaces with the particle and
mass distribution of the recent Asteroid Belt as well as estimates of the depleted
projectile and mass fraction are performed. To compare the impact-crater SFD
with the projectile’s SFD, a scaling law is applied to map the impact-crater SFD to
a projectile’s SFD. This is performed with the assumption of an average impact
velocity per planetary body, an average impact angle of 45° and an average density of
ϱ = 2.5 gcm-3 of the impactor. By integrating the chronology function derived
from impact-crater statistics on the Earth’s moon by Neukum and Ivanov (1994),
the total impacted projectiles and masses are estimated. Considering the gaps of
mean motion-resonances (MMR) of asteroids with Jupiter in the Asteroid Belt
as the dominant depletion mechanism, we compare the estimated impact-mass
with a hypothetical mass concentration of the dynamically strong 3:1 MMR of a
hypothetical pristine Asteroid Belt, and disregard other (mostly weaker) MMRs in this first
approach.
Preliminary estimates of the total count of objects with a diameter d -¥ 1Â km in the
recent Asteroid Belt (2.0 - 3.3Â AU) by this work, are in good agreement with estimates
obtained by different observational methods: (1.26 ± 0.3) -
106 by this approach, and
(1.2 ± 0.5) -
106 by an infrared-based observational approach of Tedesco and Desert
(2002). This can be compared to a total of approx. 4.3 -
106 projectiles with diameter
d -¥ 1Â km impacted on planetary surfaces in the Inner Solar System, estimated by this
work.
Early mass-estimates of the recent Asteroid Belt in the diameter range of 1.0 - 1000Â km
(Ceres included) obtained by the method described above, gives Mbelt - 3.0 -
1021Â kg,
which is also in good agreement with results obtained by an analysis of the perturbation
of the motions of the major planets due to the mass of the recent Asteroid Belt
(Krasinsky et al., 2002), which estimates Mbelt - 3.6 -
1021Â kg. For the Inner
Solar System, a total impacted mass of Min - 3.4 -
1021Â kg is obtained, roughly
4 times the mass of Ceres (MCeres - 9.35 -
1020Â kg), but this outcome is very
sensitive to impact crater-to-projectile scaling and the knowledge of the production
function towards larger crater sizes. Assuming a hypothetical, pristine Asteroid
Belt by expanding its recent highest mass concentration (kg-AU2) in the range of
2.96 - 3.276Â AU (which is assumed to be least eroded by dynamical processes
(Minton and Malhotra, 2010)) over the range of 2.0 - 3.276Â AU its estimated mass is
MBelt-un - 6.5 -
1021Â kg. The total impacted mass is roughly 1.5 times the mass
concentrated between 2.0 - 2.5Â AU of the hypothetical Asteroid Belt (close to the 3:1
MMR). Assuming the 3:1 MMR as the main dynamical depletion mechanism with a
geometrical gap-width of 0.06Â AU, the total impacted mass exceeds a hypothetical
mass residing within the gap (- 2.89 -
1020Â kg) by an order of magnitude. Those
numbers are significant higher if a loss of impactors due to dynamical extinction
(leaving the Solar System) or impacting the Sun is considered (Gladman et al.,
1997). As this early result suggests, it seems unlikely understanding the MMR
as an exclusive dynamical depletion and impactor-delivering mechanism for the
Inner Solar System, but we expect more precise results and present those at the
conference.
Acknowledgement:
The author was partly supported by the German Space Agency (DLR) with support of the
Federal Ministry of Economics and Technology, grants 50QH0305 and 50OH1102. |
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